System for magnetic deflection in cathode-ray tubes



Nov. 30, 1948. J. HAANTJES 2,455,171

SYSTEM FOR MAGNETIC DEFLECTION IN CATHODE-RAY TUBES Filed Jan. 14, 1946 JOHAN HAANTJES.

' IN V EN T 0R.

AT TORNEX Patentecl Nov. 30, 1948 SYSTEM FOR MAGNETIC DEELECTION IN CATHODE-RAY TUBES Johan Haantjes, Eindhoven, Netherlands, as-

n y mesne assignm n s, t Kantian ational Bank and Trust C m any Har ford,

Cnn.,a tr s ApplicationJanuary =14, 1946, Serial No. i641;165 In the Netherlan s e em r $8,, 1 13 Section 1, Public Law 6 90, August 3, 1946 Patent expires September '8, 1963 .3 C aims.- 1

This invention relates to a magnetic deflecting system for cathode-ray tubes, more particularly for television reproduction.

Magnetic deflection of :the electronic beam in a cathode-ray tube involves several projection faults. Of these faults the asti matism and the coma are most interfering since little or no spherical aberration occurs and :the (distortion is, as a rule, compensated by the curvature of the screen of the tube.

Astigmatism and coma occur when the electronic beam is deflected from the axial direction and become manifest in a widening of the luminous spot on the screen, resulting in the image being rendered-un sharp.

Now, the present invention provides a means whereby the occurrence of the said projection faults with magnetic deflection is suppressed wholly or in part.

According to the invention, the deflecting system is given such an asymmetric shape with respect to a plane normal to the axis Of the tube that the image is wholly or substantially wholly free from astigmatism and coma.

When using deflecting coils surrounding the cathode-ray tube this may be achieved, for example, by realizing the deflecting system in such manner that those portions of the system which are nearest to the screen of the tube are on the average more remote from the plane of symmetry of the system passing through the axis of the tube than the portions of the system which are most remote from the screen.

When use is made of deflecting coils which are plane or substantially plane the arrangement may be such that the portions of the deflecting system which are nearest to the screen of the tube are on the average also nearer to the axis of the tube than the portions of the system which are most remote from the screen.

The deflecting coils of the deflecting system are preferably so realized as to exhibit an asymmetric shape with respect to the mean norfnal plane to their axis.

It has previously been endeavored in cathoderay tubes with magnetic deflection to suppress the astigmatism and the coma. It has been endeavored to achieve this, however, with the aid of symmetric deflecting coils having such a complicated shape that the regulation and adjustment necessary for the suppression of the astigmatism and the coma cannot be efiected easily.

The invention will be explained more fully by reference to the accompanying drawing showing, by way of examples, two embodiments thereof,

2 Figures 1 and 2 being-perspectiveviews-of said embodiments.

Fig. '1 shows -a cathode-ray tube 1 having a screen .2 and a magnetic deflecting system 3; the trajectory-of the electron -beam deflected iromthe axial direction of the tubegis indicated byA.

I heusual magnetic 'deflectingisystems are constltuted by two square or rectangular coils, in general coils having a plane of-symmetrynormal to the axis of the tube. The projection obtained with the aid of such .coils always exhibits astigmatism and coma so that the reproduction on the screen is not sharp or clear. Now, itcan be deduced that these two projection faults are avoidable when the course of the magnetic field of the coils satisfies two complicated conditions, which otherwise will not "be gone further into in this description.

According to the invention, these conditions may be fulfilled by realizing the deflecting system so as to exhibit an asymmetric shape with respect to any arbitrarily chosen plane normal to the axis of the tube. In the constructional example shown in Fig. 1 the coils of the system have a plane trapezoidal shape; by suitably proportiom'ng the trapezium (and if necessary the spacing of the two coils) it may be ensured that the astigmatism as well as the coma which otherwise would occur in the projection are suppressed wholly or substantially wholly.

The deflecting system according to the invention may, however, exhibit a plane of symmetry passing through the axis of the tube. In the present case such a plane of symmetry exists, viz., the plane extending through the axis in parallel with the two coils. All the parts of the coils as thus far described are equally remote from this plane of symmetry. Now, the deflecting system, according to the invention, is realized in such manner that those portions of the coil which are near est to the screen 2 of the tube are on the average also nearer to the axis of the tube than the portions which are most remote from the screen.

Fig. 2 shows a constructional example similar to that of Fig. 1. In this case, however, the two coils of the deflecting system are not plane but are bent to surround the tube. Assuming the tube to be cylindrical at the place of the coils, all the portions of the coil are equally remote from the axis of the tube. In this case the coils are given such a shape that the portions of the deflectin system which are most adjacent to the screen of the tube are on the average more remote from the plane of symmetry through the axis than the por- 3. tions of the system which are most remote from the screen.

As shown in the constructional examples, the asymmetry of the deflecting system may be achieved by utilizing asymmetric coils. However, the asymmetry may alternatively be obtained by an asymmetric arrangement of coils which are symmetric in themselves. It is also possible to utilize, for example, coils the turns of which are distributed asymmetrically over a surface.

The constructional examples show only one defleeting system with the aid of which the electron beam can consequently be deflected in only one definite plane. As a rule, a cathode-ray tube is provided with two such systems normal .to each other. It is evident that for the other deflecting system use may be made, if desired, of an electrostatic deflection.

What I claim is:

1. A magnetic deflecting system for a cathode ray tube having means directing an electron beam along a longitudinal axis and having electron beam receiving means at one end thereof, comprising two deflecting coils surrounding the axis, each said coil being symmetrical to the other with respect to a plane through said axis and each having a first end portion closer to said electron beam receiving means and a second end portion farther from said electron beam receiving means,

said first end portions being separated by a gap different in magnitude from the gap separating said second end portions.

2. A magnetic deflecting system for a cathode ray tube having a longitudinal axis and having electron beam receiving means at one end thereof, comprising two deflecting coils surrounding the cathode ray tube, each said coil being sym- Number 4 metrical to the other with respect to a plane through said axis and each having a, first end portion closer to said electron beam receiving means and a second end portion farther from said electron beam receiving means, said first end portions being separated by a gap greater than the separation between said second end portions.

3. A magnetic deflecting system for a cathode ray tube having a longitudinal axis and havin electron beam receiving means at one end thereof, comprising two deflecting coils surrounding the cathode ray tube, each said coil being symmetrical to the other with respect to a plane through said axis and each having a first end portion closer to said electron beam receiving means and a second end portion farther from said electron beam receiving means, said second end portions being separated by a gap greater than the separation between said first end portions.

J-OHAN HAANTJES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Ruska July 2, 1940 Bowman-\dinifold et a1 Oct. 11, 1938 Blumlein June 3, 1941 Clavier et a1 July 14, 1942 Flechslg June 1, 1943 FOREIGN PATENTS Country Date Great Britain Oct. 15, 1936 Number 

